Just had a thought!

[IwannaSportSedan]

You just don't get it, do you? Or are you trying to be obstinate?

 

For someone who bemoans the idea of larger sway-bars because the stock ones are just fine, and larger ones would absolutely destroy ride quality in the hair-strand-fine tuning of the Spec B by infallible subaru engineers, you surely don't seem to grasp the theory beyond "^ Stiffer springs, less roll."

 

Stiffer springs would impact ride quality MUCH more than a couple of millimeters more diameter in the anti-roll bars.

 

Courtesy of this thread: http://legacygt.com/forums/showthread.php?t=20198

 

Coil spring Rate for the GT (Spec b is probably different, but very very close), Front, Rear in Kg of force per mm of spring compression

Stock - 3.5, 5.5

STI 'pinks' - 4.0, 6.0

Progress - 3.5, 5.8

Swift - 4.25, 6.6

Ion - 4.0-5.2, 6.7 - front is progressive wound

Tein - 6.0, 7.0

 

And courtesy of this quickly looked up page, and contributor Robert Fogt: http://www.onlineconversion.com/forum/forum_1110951659.htm

 

1 pound = 0.45359237 kilogram

1 inch = 25.4 millimeter

0.45359237/25.4 = 0.0178579673228346

 

The conversion factor is 0.0178579673228346

 

So, to convert lb/in to kg/mm you multiply by 0.0179 and to convert kg/mm to lb/in you divide by 0.0179

 

---

So the list becomes the following in lbs of force per inch of compression:

Stock - 196.0, 308.0

STI 'pinks' - 224.0, 336.0

Progress - 196.0, 324.8

Swift - 238.0, 369.6

Ion - 224.0-291.2, 375.2 - front is progressive wound

Tein - 336.0, 392.0

 

As you can see, ALL of the aftermarket springs, especially the rear, are significantly stiffer than stock by a decent margin. Progress front springs are the same as stock, but others are stiffer. And that is only the force increase to compress the suspension one mm, or one inch, respectively. That increase applies to every millimeter or inch that the spring is compressed.

 

Stiffer springs create more resistance than a few millimeters of anti-roll bar increase. I can't find easy information about the deflection angles or rates of the bars themselves, other than being rated by their diameter, which I have mentioned in previous posts.

 

I'd much rather add roll stiffness with a few millimeters of anchored anti-roll bar and keep the coil spring rates closer to stock levels, than leave the bars stock, and try to add a lot of coil spring rate to counter chassis roll with only one side of the suspension.

 

Adding coil spring rate will make the car harsher much moreso than adding anti-roll bar spring rate, for reasons I have laid out before, as well as the poor handling behavior of bottoming out too early if the spring rate is too low, or rolling over the tires if the spring rate is too high.

 

And even if your assertion is true that even with the noticeable body roll, the Spec B compared favorably to other cars, that doesn't imply that lessening the Spec B, or the GT's roll behavior won't increase handling performance even further, and it also doesn't imply that ride quality must be noticeably negatively affected by it.

 

On the other hand, really stiff coil springs, will negatively effect ride quality, even if the thinner bars technically might allow a theoretical and probably unnoticeable amount more suspension independence than the stiffer bar alternatives.

 

[austin powers voice] ... and I'm spent. [/austin powers] If you refuse to learn more than 4-syllable suspension theories, then all the facts in the realm of automotive engineering won't help you understand.

[Vimy101]

^ I appreciate the effort you are putting in but I do "get it" and "had it" from the start.

[IwannaSportSedan]

I'm done here...

 

If you think there is terrible ride quality detriments to thicker anti roll bars, but that increasing coil spring rates are the way to tune roll behavior, which is what you have been saying, then have fun not understanding.

[Vimy101]

^

 

I have been saying I'm staying with the excellent Spec.B OEM set up. The springs, sways and inverted struts provide a sweet and responsive ride.

[IwannaSportSedan]

That is not all that you have been saying, and if it were, this thread would be less than half as long.

 

You have been saying that you think that any modification from stock spec b settings, like thicker anti-roll bars, would be a detriment to ride quality and handling. I disagree.

 

I have been saying that the Legacy, even the spec B, can be improved even further.

 

I repeatedly said that I don't disagree that the stock ride is good. I haven't even criticized your desire to stay stock. I have criticized your understanding of suspension mechanics, because of the overly simplistic comments you make.

 

I just don't think that stock = the best possible. I think there is more potential there with a bit more tuning, and if Subaru did it themselves before the sale it might be a good thing, especially considering the ride height increase on the spec B, when most other sport packages lower ride height, and stiffen roll response.

 

This whole thread started, a long time ago, about someone thinking that Subaru might be further developing the Legacy. You don't seem to think that is possible or desireable. I think that development is desirable, and nearly necessary to continue competing in the market the Legacy, especially the Spec B finds itself in.

 

You say you are an infiniti fan, yet the new G35 sedan, as well as the newly revised A4, and upcoming rumored TSX with turbo and SH-AWD, are probably going to continue to eat the Legacy's lunch, in the marketplace, without much resistance from SOA, and the Spec B's 'sweet and responsive ride' is not enough to keep the Legacy afloat. It needs more. More performance at the very least.

[Vimy101]

The mechanical principles involved are quite straightforward. I fully understand them.

 

Perhaps we got a bit off track (pardon the pun) but I know how struts, springs, bushings, sway bar, links, etc. all work in concert. It's getting them in tune that is the tricky bit. If I were to do any suspension mod, it might be to go JDM Spec. I would only go OEM because I have a great deal of respect for the engineers, race team crews and designers (and their budget (and yes I know accountants have the final say)) who put together the Spec. suspension .

 

Mod the hell out of your car, best of luck and happy motoring. Let us now how it goes. Stay stock stay happy.

[psi365]

The following is a response from one of my friend's who is an automotive engineer for AC Delco who's actual part he designs is sway bar links. Now he is an automotive engineer so if you don't believe an actual expert then honestly you need to think about going back to your home planet.

 

The thread looks pretty complicated and it is late, so I really didn't read any of it.

 

How a suspension works is simple really, the 4 corners are allowed to articulate with suspension (control arms, linkages, etc) and the springs and dampers control the movement. The springs produce the force (wheel rate) that supports the vehicle mass in both static (setting still) and dynamic (a handling maneuver like going around a corner or a ride maneuver like going over a bump) so that the suspension does not bottom out. The dampers (shocks and/or struts) are added to control the movement. They actually function as timers in the system, for example to slow the springiness' of the springs so the car does not continue to bounce after going over a bump in a ride maneuver and also to slow the forces as they try to compress the springs in a handling maneuver.

 

Suspension tuning is a delicate balance to get the optimum balance of ride and handling. For better handling, stiffer springs and dampers help, however hey will negatively impact ride. For better ride, softer springs and dampers are needed... think about how a Buick Park Avenue rides more like a barge than a car. Also, think of everything as a spring. The control arm bushings for example are made out of rubber so that they provide isolation. The aftermarket provides urethane bushings which promote better handling. This is because they are stiffer springs, and being stiffer, they will negatively affect ride as well.

 

Where do stabilizer bars come in? The 'experts' in the industry say that a well tuned suspension system does not need stabilizer bars. If the correct geometry is used and the springs and dampers are chosen then a bar is not needed. Panoz did this with their Roadster, in part to prove a point. With everything, there is compromise, and the same is true with the relationship between ride and handling. Panoz made a roadster which handles very well, however it would not be appealing to a long time Buick owner, and not just because it does not have a roof. Stabilizer bars are used to add supplemental wheel rate to the suspension system so that softer springs can be used to allow for better ride. Some automotive companies do it differently. Some use stiff springs and small stabilizer bars. Others use really soft springs and large bars. The wheel rate of a suspension is the combination of the springs and the bar. The springs wheel rate contribution accommodates both ride and handling, while the bar only accommodates handling.

 

The real benefit of stabilizer bars, especially when front and rear bars are both used, is to tune the dynamic roll characteristics of a vehicle. The total wheel rate of a suspension is the addition of the spring rate and the supplemental spring rate added by the bar. When the wheel rate is referenced to a body roll angle, a roll rate (or roll stiffness) is the result. The front and rear suspensions are de-coupled (independent), so the front and rear each have independent roll stiffness. The balance between front to rear is what is tuned to control how neutral a vehicle is in a dynamic handling maneuver. If the front roll stiffness is stiffer than the rear then the car will tend to push (understeer) into a corner. If the rear roll stiffness is stiffer than the front then the car will tend to oversteer in a corner. So if you have a car that understeers, it needs more rear stiffness or less front stiffness. And for a car that oversteers you need more front stiffness or less rear stiffness. The stiffness can be adjusted with either changing springs (primary wheel rate) or the bars (supplemental wheel rate). Usually the wheel rate contribution of the bars is less than the primary wheel rate, so they are typically adjusted to fine tune the suspension. Dampers can be adjusted accordingly to time when the understeer or oversteer occur in a given maneuver.

 

That's the basics of how springs work together. Throttle and braking also come into play as well as the driveline layout RWD, FWD or AWD as the center of gravity moves around, but that is a whole other discussion that would require some diagrams. I hope this helps.

 

Thanks,

JT

SDAC-Chicago - President

 

OK so I'm on another forum where an individual won't take it that he is wrong. The debate came over what is the main purpose of what a coil spring and what the main purpose a sway bar is for. I'm pretty damn positive that I know what the purposes are, but he seems to believe that his knowledge is greater then a lot of people's. Being the fact that I know you are an engineer that deals with sway bar links you would be an expert. He also seems to believe that ride quality would greatly suffer from adding thicker sway bars. So could I get your take on this? May I also quote you on it?

 

 

Chris

[IwannaSportSedan]

very interesting reading. straight from a source authority, as it were.

[IwannaSportSedan]

he doesn't, and if I did earlier, I was mistaken, and it isn't quite what I meant to convey.

 

But it does remain that a small bump (ride event) doesn't put all that much energy into the sway bar, but more into the primary wheel rate (coil spring) to upset the other side. the other side has it's own mass and inertia, which would take a lot of energy to really move.

 

a small bump might impact the sway bar and start to twist it, but it isn't going to lift the offside wheel or really even unweight it much at all. It is true that it is anchored to the other side. That doesn't mean it automatically MOVES the other side of the suspension whenever it encounters a ride event. with one side weighted (not compressing or extending), and the other side moving over a bump, or a dip, if it is big enough for the swaybar to come into play, (not just move the linkage a bit) it just twists the bar against the other end, constrained by the chassis mounts.

 

It is anchored, but the off side isn't really impacted, just a couple of pounds of torque from the bar, not enough to overcome the unsprung weight, and then the spring rate of the that coil spring, and the damping effect of the shock/strut. That is a lot of resistance to overcome, when the input is pretty comparatively small and quick on the affected side.

 

You could kick the tire with all of your might, even magically from the bottom directly upward, and you would still probably break your foot before moving that suspension much. You know how heavy just a wheel and tire are, add the weight of the brakes, and other parts, AND a spring rate and a damper's inherent resistance. That mass will absorb a lot of energy being put in from a compressible spring input...

 

The wheel rate is fast, but short in duration and movement. and movement of the links on their joints does absorb some of that kinetic energy. (otherwise links would be solid, or with very hard bushings.

 

The supplemental roll rate adds more to a handling event with a lower speed, longer duration and distance wheel rate movement than a short, quick wheel rate movement.

 

I didn't know that the Panoz Esperante (wasn't that the name of the roadster? or both the roadster and coupe...) didn't have anti-roll bars. Ironic that it shares engine and other parts with a Mustang, which is mostly built with a live axle, aside from a few SVT Cobras.

 

The Panoz suspension must have been truly something interesting, and a major component to the design of the car. To design something like that, from what the automotive engineer says, one would almost have to design the rest of the chassis around the ideal suspension, not the other way around.

 

I also like the Dax suspension system from england... they build Lotus seven replicas with an inventive anti-roll, anti-camber-change suspension that acts more like pushrods between the coil-over perches. It is an alternative to anti-roll bar torsion springs, and keeps camber closer to constant through the wheel motion arc. (it does look more challenging to package, though.)

 

http://www.daxcars.co.uk/anti-roll-suspension-01.htm

http://www.daxcars.co.uk/images/CC&AR-0.jpg

[Vimy101]

Where in that does he say that the sway bar does not pass movement from one side of the car to the other?

 

 

He does say it:

 

"The total wheel rate of a suspension is the addition of the spring rate and the supplemental spring rate added by the bar."

[Vimy101]

he doesn't, and if I did earlier, I was mistaken, and it isn't quite what I meant to convey.

 

But it does remain that a small bump (ride event) doesn't put all that much energy into the sway bar, but more into the primary wheel rate (coil spring) to upset the other side. the other side has it's own mass and inertia, which would take a lot of energy to really move.

 

a small bump might impact the sway bar and start to twist it, but it isn't going to lift the offside wheel or really even unweight it much at all. It is true that it is anchored to the other side. That doesn't mean it automatically MOVES the other side of the suspension whenever it encounters a ride event. with one side weighted (not compressing or extending), and the other side moving over a bump, or a dip, if it is big enough for the swaybar to come into play, (not just move the linkage a bit) it just twists the bar against the other end, constrained by the chassis mounts.

 

It is anchored, but the off side isn't really impacted, just a couple of pounds of torque from the bar, not enough to overcome the unsprung weight, and then the spring rate of the that coil spring, and the damping effect of the shock/strut. That is a lot of resistance to overcome, when the input is pretty comparatively small and quick on the affected side.

 

You could kick the tire with all of your might, even magically from the bottom directly upward, and you would still probably break your foot before moving that suspension much. You know how heavy just a wheel and tire are, add the weight of the brakes, and other parts, AND a spring rate and a damper's inherent resistance. That mass will absorb a lot of energy being put in from a compressible spring input...

 

The wheel rate is fast, but short in duration and movement. and movement of the links on their joints does absorb some of that kinetic energy. (otherwise links would be solid, or with very hard bushings.

 

The supplemental roll rate adds more to a handling event with a lower speed, longer duration and distance wheel rate movement than a short, quick wheel rate movement.

 

I didn't know that the Panoz Esperante didn't have anti-roll bars. Ironic that it shares engine and other parts with a Mustang, which is mostly built with a live axle, aside from a few SVT Cobras.

 

The Panoz suspension must have been truly something interesting, and a major component to the design of the car. To design something like that, from what the automotive engineer says, one would almost have to design the rest of the chassis around the ideal suspension, not the other way around.

 

I also like the Dax suspension system from england... they build Lotus seven replicas with an inventive anti-roll, anti-camber-change suspension that acts more like pushrods between the coil-over perches. It is an alternative to anti-roll bar torsion springs, and keeps camber closer to constant through the wheel motion arc. (it does look more challenging to package, though.)

 

http://www.daxcars.co.uk/anti-roll-suspension-01.htm

http://www.daxcars.co.uk/images/CC&AR-0.jpg

 

"The total wheel rate of a suspension is the addition of the spring rate and the supplemental spring rate added by the bar."

A sway bar connects one independent to another.

That excellent contribution describes succinctly and efficiently how suspension systems work.

However, when the writer says stiffer bushings give better performance, I have to say true but with big caveats. Stiffer bushings will translate into more precise steering inputs, for instance, but at cost. Bushings are like tiny shock absorbers. If you have a track car on a nice surface, it's one thing. If you are on a city street or cruising on a freeway, it's another.

[Vimy101]

 

You could kick the tire with all of your might, even magically from the bottom directly upward, and you would still probably break your foot before moving that suspension much. You know how heavy just a wheel and tire are, add the weight of the brakes, and other parts, AND a spring rate and a damper's inherent resistance. That mass will absorb a lot of energy being put in from a compressible spring input...

 

 

 

This is where unsprung weight comes into play. The Spec.B suspension directly addresses this key factor. Even the struts are inverted.

[IwannaSportSedan]

It may have less unsprung weight... that may be true.

 

but I'll bet you'd still break your foot kicking it, before the suspension would really move. Still some significant weight in play.

[Vimy101]

^ There is at least one magnitude order of difference involved in hitting a pothole at speed. Forces increase exponentially at a 40 mph velocity on an asphalt patched surface at .5 lateral G. "An object in motion tends to stay in motion unless acted upon by an outside source." (or something to that effect).

[mand3j]

d@mn, you guys crack me up...

I couldn't talk that much in a month, let alone write that much.

[Vimy101]

d@mn, you guys crack me up...

I couldn't talk that much in a month, let alone write that much.

 

My posts are short.

[mand3j]

My posts are short.

 

6000+ posts????

Naaa, I ain't taking the bait.

 

Arguing with you would be as smart as stepping into the ring with Mike Tyson.

[whobaru]

"An object in motion tends to stay in motion unless acted upon by an outside force."

 

fixored

[mand3j]

Oh yeah, I did have a thought...

 

I wouldn't be shocked if the Leggys were discontinued in the states.

Not much press/development/or sales since 05'.

I also saw a blurb in Road & Track where they made an experimental

7 passenger Leggy/forester combo wagon.

 

My bet is the Leggy goes away for a year and something new is announced in 09

[Vimy101]

^ Good tires are the best thing you can do for an LGT. Two sets. Summer and winter.

[Vimy101]

fixored

 

Thanks. (Though source of the force might be a pothole.)

 

Got Newton's basic laws of motion handy for us?

[whobaru]

no, but I'm sure our friend google does.

[Vimy101]

no, but I'm sure our friend google does.

 

I'll put them up and some one will accuse me of implying that the Spec.B (Spec.V?) is "Teh King of Cars".

[whobaru]

not after the spec-b kicks in yo!

[Vimy101]

not after the spec-b kicks in yo!

 

Spec.B doesn't "kick in". You pay for it up front.